A physical pendulum consists of a meter stick that is pivoted at a small hole drilled through the stick a distance x from the 50 cm mark. The period of oscillation is observed to be 4.8 s. Find the distance x. m

Respuesta :

Answer:

x=0.01457 m

Explanation:

From parallel axis theorem

I=Icm+mh²

where h=x

The rotational inertia about its center of mass is

Icm=mL²/12

where L=1.0 m

Thus T=4.8s  we obtain

[tex]T=2\pi \sqrt{\frac{mL^{2}/12+mx^{2}  }{mgx} }\\ T=2\pi \sqrt{\frac{L^{2} }{12gx}+x/g }\\ T^{2}=4\pi^{2}(\frac{L^{2} }{12gx}+x/g )/x\\ T^{2}x=\frac{\pi^{2} L^{2} }{3g}+(\frac{4\pi^{2} }{g})x^{2}\\   0=(\frac{4\pi^{2}  }{g} )x^{2}-(T^{2} )x+(\frac{\pi^{2}L^{2}   }{3g} )\\ 4.03x^{2}-23.04x+0.335=0[/tex]

After Solving this quadratic we get

x₁=5.702 m

x₂=0.01457 m

One of the solution is an impossible value for x (x=5.70m is greater than L)

So we choose the other one

x=0.01457 m

The distance x at which the hole is located from the 50 cm mark is; x = 15 cm

We are given;

period; T = 4.8s

The formula for period here is;

T = 2π√(I/mgh)

where;

T is period

I is moment of inertia

m is mass

g is acceleration due to gravity

h is the same as the distance x we are looking for

Now, from parallel axis theorem, moment of inertia is;

I = I_cm + mx²

where;

I_cm = ¹/₁₂mL²

where L is generally equal to 1. Thus;

I_cm = ¹/₁₂m

Thus;

I = ¹/₁₂m + mx²

Put ¹/₁₂m + mx² for I in the period equation to arrive at;

T = 2π√[(1/12gx) + (x/g)]

Simplifying this to a quadratic form gives;

(4π²/g)x² - T²x + (π²/3g)

Putting 4.8 for T and 9.8 for g gives;

4.028x² - 23.04x + 0.3357 = 0

Using online quadratic equation solver , we have;

x = 5.705m or 0.015m

Since the hole is at a distance x from the 50 cm mark, then x cannot be 5.705 but will be 0.015.

Thus;

x = 0.015m or 15 cm

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